Insulated anode for cathode-ray tubes



Sept. 26, 1950 M. P. WILDER INSULATED ANODE FOR CATHODE-RAY- TUBES FiledJune 25, 1949 INVENTOR MARSHALL P. WILDER ATTORNEY Patented Sept. 26,1950 UNITED STATES PATENT OFFICE.

INSULATED ANODE FOR CATHODE RAY I I I UBES" Marshall P. Wilder,Stamford, Conn, assignor to Remington Rand Inc., New York, N. Y., acorporation of Delaware Application J une25, 1949, Serial No. 101,283

7 2 Claims. 1

This invention relates to cathode ray tubes,

and has particular reference to the structural. mounting of av highvoltage anode for those tubeswhichhave metallic envelopes.

The conventional design of. cathode ray tubes includes an envelope ofglass, an electron emitting device, generally called an electron gun, anenlarged volume into which the cathode ray is projected, and an. endvface. plate which. is coated with a fil'm. of. luminescent material-Electrons, generated and projected by the electron gu-n,pass intotheenlarged volume: where they may be deflected to form a pattern andfinally strike the luminescent material which is caused to fluoresce andshow a visible picture. g

The enlarged volume is often formed in a-conical shape and the envelopematerial may be either of glass or metal. If itis made of glass, orother insulating material, the inside surface isxcovered with anon-reflectingconductive coating: to which a positive potential ofseveral kilovolts above cathode potential is applied. This conductivecoating serves several. purposes. It aids in accelerating the electronbeam toward the screen; secondary electrons formed at the screen areabsorbed; and light reflections from the screen are also absorbed.

The outside of the glass envelope is often covered with a conductinglayer and grounded to help screen the tube from outside electrostaticfields and to form a capacitorto be used in a filter circuit.

If a metallic sleeve is used for all or part of the enlarged portion ofthe envelope, no inside conductive coating is necessary since the metalitself serves the purpose. In addition, the metal sleeve is opaque andcan easily be made with a non-reflecting inside surface.

A metal sleeve having a positive potential of several kilovolts aboveground creates many insulating problems especially when the tube ismounted inside a cabinet with associated circuit equipment in'closeproximity. Also the absence of the filter capacitor requires anotherhigh voltage component to be added to the equipment.

The present invention includes a new design for cathode ray tubes usinga metallic sleeve as part of the tube envelope. A second conductingsleeve is mounted inside the first, having about the same shape butuniformly spaced therefrom and mounted on insulating spacers. The outermetal sleeve, which is sealed vacuum tight to the rest of the envelopematerial, is operated at ground potential. The inner metal sleeve isex-One object of the inventionis to provide a cathode ray tube of improveddesign. which avoids one or more of the disadvantages, and limitationsof prior art arrangements.

Another object of this invention is to improve present day cathode raytubes having meta1lic sleeves so that both the sleeve and the cathodemaybe operated at ground potential.

Another object of the invention is to provide a cathode ray tube havinga predetermined builtin filter capacitor... j

For a better understandin ofthe.v presentinvention, together with otherand further objects thereof, reference. is made to thefollowi'nggdescription taken in connection with the .accom-j lpanying drawings. 7 l

Fig. l is a longitudinal cros'ssectionof a oath-.- ode ray tubeaccording to theinvention Fig. 2 is a cross sectional View of. thetubeofFig, 1,. taken alongline 22. of'that figure. Referring now to Fig.1,,a..glass neck' [0. is employed to house. theelectron gun I l whichmay be-of conventional construction. At the. screen endof the neck anenlargedor bell-shapedportion 12 is: formed to act as the:supportingbase for a conductive coating I3.; The rim of the enlarged.portion I 2..is.sea1edto a, metallic sleeve l4 which is generallyconical in shape. At the large end of the sleeve M. a transparent glassplate [5 is. mounted With-its rim sealed to the edgeof the sleeve. Theinside surface of the glass plate I5 is coated with fluorescent materiall6 as is usual in the construction of cathode ray tubes.

Inside the metallic sleeve and generally parallel to it is mounted asecond metallic sleeve 11. To provide the proper spacing and electricalinsulation, small ceramic insulators is are positioned between the twosleeves. The dilference of potential between the two sleeves l4 and I1may .2 as great as 40 kilovolts, but since the inner .leeve issurrounded by a vacuum, the distarfe between them need not be more thanof an inch.

At the small end of the inner sleeve l'l, three springs 20 are securedby Welding or riveting. The springs extend beyond the rim of the sleevel4 so that when the tube is completely assembled, the ends of thesprings make contact with the conductive coating I3. A conductivelead-in wire I9 is mounted in the bell-shaped portion [2 to apply a highpotential to coating I3 and sleeve ll.

At the large end of inner sleeve l! a second set of springs 2| ismounted to make conductive con- 3 tact with the fluorescent coating I6.A small conductive terminal lug 2-5 is Welded to the outside surface ofsleeve M to facilitate the connection to ground and the negativeterminal of a source of high potential.

The tube is assembled in the following manner: First, the inner sleeveI1 is placed in the outer sleeve I4 and secured by fastening theinsulator blocks to each sleeve. Second, the face plate I5, without thefluorescent screen [6, is placed on the end flange of sleeve I4 and themetal-to-glass seal 23 is made. Third, the neck I0, without the electrongun, is sealed to the flange 22 at the small end of sleeve I4. At thispoint all the major components have been assembled in a singlearrangement. Next, the fluorescent screen material I6 is added and theconductive coating I3 is painted on the inside of volume I2.

The tube is now ready for the final assembly operations. The entirearrangement is baked to remove all traces of moisture; then the electrongun II is mounted in the neck I; the tube is exhausted, processed, andsealed.

The operation of the tube is the same as the usual form of cathode raytube except that the outer sleeve I4 is grounded and the inner sleeve II is kept at a high potential by means of a battery 26 or otherconvenient source. Electrical connection for the inner sleeve is made bymeans of the lead-in terminal I9, springs and conductive coating I3.

Since the double sleeve is to be used as a capacitor in a filtercircuit, it is essential that the desired capacity be achieved withinreasonable limits. This may be accomplished by carefully gauging theinsulated spacers l8 and holding the area of the inner sleeve to closelimits. In case a change of circuit constants demands a change of filtercapacity, the new value may be easily obtained by using an altered setof spacers.

, While there have been described and illustrated specific embodimentsof the invention, it will be obvious that various changes andmodifications may be made therein without departing from the field ofthe invention which should be limited only by the scope of the appendedclaims.

What is claimed is:

1. A cathode ray tube comprising, a tube envelope for enclosing andsupporting an electron gun at one end and a fluorescent screen at theopposite end, an outer metallic sleeve forming part of the envelopeadjacent to the fluorescent screen, a connection between the outersleeve and ground, an inner metallic sleeve mounted in parallelrelationship to the outer sleeve, a connection between the inner sleeveand a source of high positive potential, a plurality of springconnectors secured to the inner sleeve and projecting longitudinally tomake contact with the fluorescent screen, and fixed insulator supportsbetween the inner and outer sleeves for securing the inner sleeve inposition.

2. A cathode ray tube comprising, a tube envelope for enclosing andsupporting an electron gun at one end and a fluorescent screen at theopposite end, a conductive coating mounted on the inside of saidenvelope adjacent the electron gun, a connection between the conductivecoating and a source of high positive potential, an outer metallicsleeve forming part of the envelope adjacent to the fluorescent screen,a connection between the outer sleeve and ground, an inner metallicsleeve mounted in parallel relationship to the outer sleeve, a pluralityof spring connectors secured to the inner sleeve and projectinglongitudinally to make contact with the fluorescent screen, one or morespring connectors secured to the inner sleeve and projectinglongitudinally to make contact with the conductive coating, and fixedinsulator supports between the inner and outer sleeves for securing theinner sleeve in position.

MARSHALL P. WILDER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

